1. Field of the Invention
The present invention relates to a developing device of an electrostatic developing device and, more particularly, to a developing device of an electrostatic apparatus such as an electrostatic copying machine or a laser printer.
2. Description of Related Art
A prior art electrostatic apparatus employs a pseudo two-component developing system using a developer consisting of a magnetic toner and a magnetic carrier. A process cartridge 51 for the pseudo two-component developing system will be described with reference to FIG. 7.
The process cartridge 51 comprises a photoconductive drum 52, a charger 54, a cleaning blade 58 and a developing unit 63 comprising a developing sleeve 56 internally provided with a magnet roller 60, a developer container 64 containing a developer 66, and a doctor blade 62 disposed above the developing sleeve 56. The charger 54, the developing sleeve 56 and the cleaning blade 58 are arranged in that order around the photoconductive drum 52 along the direction of rotation of the photoconductive drum 52 indicated by the arrow z. The developer 66 is, for example, a mixture of a magnetic toner and a magnetic carrier, having a magnetic toner content of about 40% by weight and a magnetic carrier content of about 60% by weight.
In the process cartridge 51 thus constructed, the developing sleeve 56 is rotated in the direction of the arrow x, and the magnet roller 60 is rotated in the direction of the arrow y. Then, the developer 66 adheres to the circumference of the developing sleeve 56, the doctor blade 62 regulates the amount of the developer 66 on the circumference of the developing sleeve 56 so that a layer of the developer 66 of a predetermined thickness is formed over the circumference of the developing sleeve 56. The layer of the developer 66 of the predetermined thickness is carried to a developing point 50 between the photoconductive drum 52 and the developing sleeve 56 by the rotating developing sleeve 56.
Since the developing sleeve 56 and the magnet roller 60 rotate respectively in opposite directions, the S-poles and the N-poles of the magnet roller 60 move at a considerably high speed relative to the developer 66 coating the circumference of the developing sleeve 56. Hence, the polarity of the magnetic field applied to the developer 66 changes rapidly. Consequently, as shown in FIG. 8, brushes 66A of the developer 66 roll on the circumference of the developing sleeve 56 as the same are carried toward the developing point 50.
At the developing point 50, only the magnetic toner is transferred to the photoconductive drum 52 according to an image formed on the photoconductive drum 52. The magnetic carrier remains on the circumference of the developing sleeve 56. The magnetic carrier remaining on the circumference of the developing sleeve 56 is returned to the developer container 64. Thus, the developer 66 is charged as it passes the gap between the developing sleeve 56 and the doctor blade 62 and rolls on the circumference of the developing sleeve 56.
When developing an image by the pseudo two-component developing system, the quality of the developed image is dependent on the ratio between the magnetic toner content and the magnetic carrier content of the developer 66 coating the circumference of the developing sleeve 56; the greater the percentage of the magnetic carrier content, the higher is the quality of the developed image. However, since the developing unit 63 shown in FIG. 7 contains the developer 66 (i.e., a mixture of the magnetic toner and the magnetic carrier) dispersed in the developer container 64, it is impossible to maintain a high percentage of the magnetic carrier in the vicinity of the developing sleeve 56.
A developing unit employing a pseudo two-component developing system using a magnetic toner and a magnetic carrier intended to overcome such a disadvantage is disclosed in U.S. Pat. No. 4,676,192, shown in FIG. 9. As shown in FIG. 9, in this developing unit 120, a magnetic toner container 125 and a magnetic carrier container 126 are disposed contiguously and separated from each other by a partition wall 124. A developing sleeve 56 is disposed with a gap between its circumference and the edge of the partition wall 124. The upper opening of the magnetic toner container 125 is closed by a cover 129, and the upper opening of the magnetic carrier container 126 is closed by a cover 127. When replenishing the magnetic toner container 125 and the magnetic carrier container 126 respectively with a magnetic toner and a magnetic carrier, the covers 129 and 127 are opened.
The magnetic toner is supplied to the developing sleeve 56 in a magnetic toner supply region 128, and the magnetic carrier is supplied from the magnetic carrier container 126 to the developing sleeve 56. Developer brushes are formed on the circumference of the developing sleeve 56. The height of the developer brushes is regulated by a doctor blade 62, and the developer brushes of a predetermined height are carried to a developing point 50.
The partition wall 124 prevents the magnetic carrier from flowing into the magnetic toner container 125. Hence, the magnetic carrier will not be dispersed in the magnetic toner in the magnetic toner container 125. Thus, the percentage of the magnetic carrier in the developer coating the circumference of the developing sleeve 56 can be maintained at a substantially constant high percentage, and an image formed on a photoconductive drum 52 can be developed with the developer having a high magnetic carrier percentage in a developed image of a high quality.
When using the developing unit 120 for the first time, the new developing unit 120 is set in place, the cover 127 is opened, and the magnetic carrier is supplied into the magnetic carrier container 126 in a first step. In a second step, cover 129 is opened, and the magnetic toner is supplied into the magnetic toner container 125. Thus, the developing unit 120 requires two steps to supply developer before using the unit for the first time, which is troublesome. Furthermore, there is the possibility that the operator will forget to carry out either the first step of supplying the magnetic carrier or the second step of supplying the magnetic toner. If the operator forgets to carry out the first step, an image is developed only with the magnetic toner. Consequently, the image cannot be developed in a developed image of satisfactory quality.
Such problems may be prevented by packing only the magnetic carrier in the magnetic carrier container 126 before shipping the developing unit. However, since the magnetic carrier cannot be sealed in the magnetic carrier container 126, the magnetic carrier spills out from the magnetic carrier container during transportation.